1. Field of the Invention
The present invention relates to a pump control system that has an electric energy-saving effect, used for pressurized water pump systems, air-conditioning systems, and the like.
2. Description of the Prior Art
FIG. 1 is a drawing illustrating the configuration of an example of conventional pump control system generally used from the past, in which a pump control system is used for pressurized water pump system.
In FIG. 1, primary supply pumps 1 supply chilled water or hot water from return header 2 to primary supply header 4 via refrigerators or heat pump chillers or boilers 3.
Secondary supply pumps 5 are provided with inverters 6 and supply chilled water or hot water to secondary supply header 7 from primary supply header 4.
Flow sensor 8 measures the flow rate of chilled water or hot water supplied to return header 2 via two-way type control valves 9 and heat exchangers 11 from secondary supply header 7.
Pressure difference sensor 12 measures the differential pressure of chilled water or hot water between secondary supply header 7 and return header 2.
Controller for controlling the number of operating pumps 13 issues operation commands to secondary supply pumps 5 so that the optimum number of operating pumps is obtained using values measured by flow sensor 8 and pressure difference sensor 12.
In the above configuration, chilled water or hot water delivered from primary supply pumps 1 is supplied to heat exchangers 11 at the secondary use point by secondary supply pumps 5.
The flow rate of the secondary circulating flow is variable because two-way type control valves 9 are controlled depending on the heat exchanging amounts required by heat exchangers 11.
In this case, controller for controlling the number of operating pumps 13 issues operation commands to secondary supply pumps 5 so that the optimum number of operating pumps is obtained by detecting flow rate with flow sensor 8, and at the same time sends a rotational frequency control signal to inverters 6 so that the required pre-set differential pressure is obtained by detecting the differential pressure between secondary supply header 7 and return header 2 with pressure difference sensor 12.
As a result, a pump control system that can reduce electric power consumption is obtained.
However, there are the following problems in such conventional pump control systems:    (1) The control systems are rotational frequency control systems at a constant pressure that detect the differential pressure between secondary supply header 7 and return header 2 or the pressure at secondary supply header 7 without directly detecting the required secondary water flow.    (2) They are rotational frequency control systems that, although they have an energy-saving effect accompanying the reduction of water flow, have little energy-saving effect for the head which reduces in proportion to the flow rate ratio to the second power, because they are rotational frequency control systems at a constant pressure.    (3) In addition, if the pressure setup happens to be lower, they may stabilize while the flow rate is too low for the load.    (4) The adjustment setup can be done only at the installation site. Also, since they have no function for storing historical data, adjustment to the optimum value requires separate monitoring and is difficult.    (5) Since the peak load timing varies, changes of control system parameters for responding to those timings, or for load variation due to changes of parameters in production equipment availability factor and others, are designed to be operated manually at an installation site or within the premises, in other words, operability is not good.    (6) Calculation of the energy-saving effect is laborious and time-consuming because in order to acquire data at an installation site, it is necessary to provide measuring instruments, to perform measurement, to bring back the data obtained, and then to calculate the energy-saving effect.